JP2015079561A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely reduce output voltage of a fuel cell when hydrogen leak is generated.SOLUTION: A fuel cell 10 includes a tabular membrane electrode assembly 50 and separators 34, 36 are attached to both sides of the membrane electrode assembly 50. The membrane electrode assembly 50 includes a solid polymer electrolyte membrane 20, an anode 22 and a cathode 24. The cathode 24 includes a laminate comprising a cathode catalyst layer 30, a poisoning substance generation layer 31 and a cathode gas diffusion layer 32. The poisoning substance generation layer 31 includes a compound for generating a poisoning substance for poisoning a metal catalyst included in the cathode catalyst layer 30 by reacting with hydrogen. Concretely, a thiol group is shown as the poisoning substance.

Description

  The present invention relates to a fuel cell that generates electricity by an electrochemical reaction between hydrogen and oxygen.

  In recent years, fuel cells that have high energy conversion efficiency and do not generate harmful substances due to power generation reactions have attracted attention. As one of such fuel cells, a polymer electrolyte fuel cell is known.

A polymer electrolyte fuel cell has a basic structure in which a polymer electrolyte membrane, which is an electrolyte membrane, is disposed between a fuel electrode and an air electrode. The fuel electrode contains hydrogen and the air electrode contains oxygen. It is a device that supplies the agent gas and generates power by the following electrochemical reaction.
Fuel electrode: H ₂ → 2H ⁺ + 2e ⁻ (1)
^{_{Cathode: 1 / 2O 2 + 2H +}} + 2e - → H 2 O ··· (2)
The anode and cathode each have a structure in which a catalyst layer and a gas diffusion layer are laminated. The catalyst layers of the electrodes are arranged opposite to each other with the solid polymer film interposed therebetween, thereby constituting a fuel cell. The catalyst layer is a layer formed by binding carbon particles carrying a catalyst with an ion exchange resin. The gas diffusion layer becomes a passage for the oxidant gas and the fuel gas.

  At the anode, hydrogen contained in the supplied fuel is decomposed into hydrogen ions and electrons as shown in the above formula (1). Among these, hydrogen ions move inside the solid polymer electrolyte membrane toward the air electrode, and electrons move to the air electrode through an external circuit. On the other hand, in the cathode, oxygen contained in the oxidant gas supplied to the cathode reacts with hydrogen ions and electrons that have moved from the fuel electrode, and water is generated as shown in the above formula (2). In this way, in the external circuit, electrons move from the fuel electrode toward the air electrode, so that electric power is taken out.

  In general, a sufficient gas seal is provided between the anode and the cathode. However, due to factors such as damage to the solid polymer membrane, fuel gas, that is, hydrogen gas leaks from the anode to the cathode, and the fuel cell. May impair safety. For this reason, Patent Document 1 discloses a technique for notifying a user of a leak by releasing an odor substance into a catalyst layer of an anode based on a chemical reaction of a combustible substance.

JP 2008-134228 A

  In Patent Document 1, when a hydrogen leak occurs, the user can be notified, but unless the user takes an appropriate measure against the hydrogen leak, the fuel cell generates power while the hydrogen leak itself continues. For this reason, the safety of the fuel cell at the time of hydrogen leak could not be improved reliably.

  The present invention has been made in view of these problems, and an object thereof is to provide a technique capable of reliably reducing the output voltage of a fuel cell when hydrogen leak occurs.

  One embodiment of the present invention is a fuel cell. The fuel cell includes an electrolyte membrane, an anode provided on one surface of the electrolyte membrane, and a cathode provided on the other surface of the electrolyte membrane, the cathode being a cathode catalyst layer in contact with the electrolyte membrane; Provided between the cathode gas diffusion layer, and between the cathode catalyst layer and the cathode gas diffusion layer, and reacts with hydrogen to contain a compound that generates a poisoning substance that poisons the catalytic metal contained in the cathode catalyst layer. And a toxic substance generation layer.

  According to the present invention, when a hydrogen leak occurs, the output voltage of the fuel cell can be reliably reduced.

1 is a perspective view schematically showing the structure of a fuel cell according to an embodiment. It is sectional drawing on the AA line of FIG. It is the elements on larger scale which show the layer structure of the poisoning substance production | generation layer of embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

  FIG. 1 is a perspective view schematically showing the structure of a fuel cell 10 according to an embodiment. FIG. 2 is a cross-sectional view taken along the line AA of FIG. The fuel cell 10 includes a flat membrane electrode assembly 50, and a separator 34 and a separator 36 are provided on both sides of the membrane electrode assembly 50. In this example, only one membrane electrode assembly 50 is shown, but a plurality of membrane electrode assemblies 50 may be stacked via the separator 34 or the separator 36 to constitute a fuel cell stack. The membrane electrode assembly 50 includes a solid polymer electrolyte membrane 20, an anode 22, and a cathode 24.

  The anode 22 has a laminate composed of an anode catalyst layer 26 and an anode gas diffusion layer 28. On the other hand, the cathode 24 has a laminate including a cathode catalyst layer 30, a poisoning substance generation layer 31 and a cathode gas diffusion layer 32. That is, in the present embodiment, the poisoning substance generation layer 31 is arranged in a layer between the cathode catalyst layer 30 and the cathode gas diffusion layer 32. The anode catalyst layer 26 and the cathode catalyst layer 30 are provided so as to face each other with the solid polymer electrolyte membrane 20 interposed therebetween.

  A gas flow path 38 is provided in the separator 34 provided on the anode 22 side. Fuel gas is distributed to a gas flow path 38 from a fuel supply manifold (not shown), and the fuel gas is supplied to the membrane electrode assembly 50 through the gas flow path 38.

  Similarly, a gas flow path 40 is provided in the separator 36 provided on the cathode 24 side. The oxidant gas is distributed to the gas flow path 40 from the oxidant supply manifold (not shown), and the oxidant gas is supplied to the membrane electrode assembly 50 through the gas flow path 40.

  Specifically, during operation of the fuel cell 10, a reformed gas containing a fuel gas, for example, hydrogen gas, flows through the gas flow path 38 along the surface of the anode gas diffusion layer 28 from above to below. Fuel gas is supplied to the anode 22.

  On the other hand, during operation of the fuel cell 10, an oxidant gas, for example, air flows through the gas flow path 40 from the upper side to the lower side along the surface of the cathode gas diffusion layer 32, thereby supplying the oxidant gas to the cathode 24. Is done. Thereby, a reaction occurs in the membrane electrode assembly 50. When hydrogen gas is supplied to the anode catalyst layer 26 through the anode gas diffusion layer 28, hydrogen in the gas becomes protons, and these protons move through the solid polymer electrolyte membrane 20 to the cathode 24 side. At this time, the emitted electrons move to the external circuit and flow into the cathode 24 from the external circuit. On the other hand, when air is supplied to the cathode catalyst layer 30 through the cathode gas diffusion layer 32, oxygen is combined with protons to become water. As a result, electrons flow from the anode 22 toward the cathode 24 in the external circuit, and power can be taken out.

  The solid polymer electrolyte membrane 20 exhibits good ion conductivity in a wet state, and functions as an ion exchange membrane that moves protons between the anode 22 and the cathode 24. The solid polymer electrolyte membrane 20 is formed of a solid polymer material such as a fluorine-containing polymer or a non-fluorine polymer, and is, for example, a sulfonic acid type perfluorocarbon polymer, polysulfone resin, a phosphonic acid group or a carboxylic acid group-containing perfluorocarbon polymer. A fluorocarbon polymer or the like can be used. Examples of the sulfonic acid type perfluorocarbon polymer include Nafion (manufactured by DuPont: registered trademark) 112. Examples of non-fluorine polymers include sulfonated aromatic polyetheretherketone and polysulfone. A typical film thickness of the solid polymer electrolyte membrane 20 is 50 μm.

  The anode catalyst layer 26 constituting the anode 22 is composed of an ion conductor (ion exchange resin) and carbon particles carrying a metal catalyst, that is, catalyst-carrying carbon particles. A typical film thickness of the anode catalyst layer 26 is 10 μm. The ionic conductor connects the carbon particles carrying the metal catalyst and the solid polymer electrolyte membrane 20, and has a role of transmitting protons between the two. The ionic conductor may be formed from the same polymer material as the solid polymer electrolyte membrane 20.

  The metal catalyst is, for example, an alloy catalyst made of a noble metal and ruthenium. Examples of the noble metal used for the metal catalyst include platinum and palladium. Examples of the carbon particles supporting the metal catalyst include acetylene black, ketjen black, carbon nanotube, and carbon nano-onion.

  The anode gas diffusion layer 28 constituting the anode 22 has an anode gas diffusion base material and a microporous layer applied to the anode gas diffusion base material. The anode gas diffusion base material is preferably composed of a porous body having electron conductivity, and for example, carbon paper, carbon woven fabric or nonwoven fabric can be used.

  The microporous layer applied to the anode gas diffusion base material is a paste-like kneaded product obtained by kneading a conductive powder and a water repellent. For example, carbon black can be used as the conductive powder. As the water repellent, a fluorine resin such as tetrafluoroethylene resin (PTFE) can be used. It is preferable that the water repellent has a binding property. Here, the binding property refers to a property that can be made sticky (state) by joining things that are less sticky or those that tend to break apart. Since the water repellent has binding properties, a paste can be obtained by kneading the conductive powder and the water repellent.

  The cathode catalyst layer 30 constituting the cathode 24 has one surface in contact with the solid polymer electrolyte membrane 20, and is composed of an ion conductor (ion exchange resin) and carbon particles supporting a metal catalyst, that is, catalyst-supporting carbon particles. Composed. The ionic conductor connects the carbon particles carrying the metal catalyst and the solid polymer electrolyte membrane 20, and has a role of transmitting protons between the two. The ionic conductor may be formed from the same polymer material as the solid polymer electrolyte membrane 20. Examples of the supported metal catalyst include one kind of platinum, cobalt, rhodium, palladium and the like, or an alloy of these two kinds. Examples of the carbon particles supporting the metal catalyst include acetylene black, ketjen black, carbon nanotube, and carbon nano-onion.

  The poisoning substance generation layer 31 constituting the cathode 24 is provided between the cathode catalyst layer 30 and the cathode gas diffusion layer 32. The poisoning substance generation layer 31 includes a compound that reacts with hydrogen to generate a poisoning substance that poisons the metal catalyst contained in the cathode catalyst layer 30. Specifically, examples of the poisoning substance include thiols. The poisoning substance is preferably water-soluble. According to this, the poisoning substance easily reaches the metal catalyst of the cathode catalyst layer 30, and the metal catalyst can be more reliably poisoned. The cathode catalyst layer 30 has sufficient gas permeability to air and does not hinder the supply of air from the cathode gas diffusion layer 32 to the cathode catalyst layer 30.

式(１)中、Ｍは、Ａｕ、Ｃｕ、Ｐｔから選ばれる。Ｒは、アルキル鎖などの炭素鎖を示す。Ｒ’は、アルキル基、アミノアルキル基、カルボキシル基、水酸基、スルホ基から選ばれる。なお、Ｒは、プロトン伝導性を有する官能基を有していることが好ましい。Ｒがプロトン伝導性を有する官能基を有することにより、被毒物質生成層３１のプロトン伝導性を向上させることができる。 As a compound that generates a poisoning substance, a compound represented by the following formula (1) can be used.

In formula (1), M is selected from Au, Cu, and Pt. R represents a carbon chain such as an alkyl chain. R ′ is selected from an alkyl group, an aminoalkyl group, a carboxyl group, a hydroxyl group, and a sulfo group. Note that R preferably has a functional group having proton conductivity. When R has a functional group having proton conductivity, the proton conductivity of the poisoning substance generation layer 31 can be improved.

When a hydrogen leak occurs in the membrane / electrode assembly 50 due to damage to the solid polymer electrolyte membrane 20, the following reaction proceeds in the poisoning substance generation layer 31.
MSR-S-S-R '+ H ₂ → M-S-R-SH + R'-SH
That is, R′-SH (thiols) is decomposed from MSRSRSS ′ and released as poisonous substances, and dissolved in water contained in the cathode 24. When the poisoning substance (R′-SH) dissolved in water reaches the metal catalyst of the cathode catalyst layer 30, the poisoning substance is bound to or adsorbed to the metal catalyst, thereby reducing the activity of the metal catalyst. As a result, the output voltage of the fuel cell 10 can be reduced and finally the operation of the fuel cell 10 can be stopped. From the viewpoint of increasing the water solubility of R′-SH (thiols), R ′ preferably has a hydrophilic group, and R ′ is preferably an aminoalkyl group, a carboxyl group, a hydroxyl group, or a sulfo group. Used. Specific examples of R′—SH (thiols) include 2-aminoethanethiol and ethanethiol.

  FIG. 3 is a partially enlarged view showing the layer structure of the poisoning substance generation layer 31 of the present embodiment. As shown in FIG. 3, the metal M in the formula (1) is fixed to the main surface of the cathode gas diffusion layer 32 facing the cathode catalyst layer 30. A method for fixing the metal M to the cathode gas diffusion layer 32 is not particularly limited, and examples thereof include a sputtering method and a plating method. Moreover, in this Embodiment, the monomolecular film of the said compound is formed when the said compound forms a self-organization film | membrane. By making the poisoning substance generating layer 31 a monomolecular film of the above compound, it is possible to poison the cathode catalyst metal at the time of hydrogen leakage while suppressing the decrease in conductivity due to the poisoning substance generating layer 31.

An example of a method for forming the poisoning substance generation layer 31 made of a monomolecular film of the above compound as shown in FIG. 3 is as follows.
(1) A metal thin film (for example, an Au thin film) is formed on the main surface of the cathode gas diffusion layer 32 by sputtering.
(2) In order to remove organic substances on the surface of the metal thin film, cleaning is performed using pure water.
(3) Number of thiols represented by HS—R—S—S—R ′ (R and R ′ are the same as R and R ′ included in M—R—S—S—R ′) Immerse in an ethanol solution of tens of μmol / l for a predetermined time. Thereby, a self-assembled monomolecular film of a thiol chain (—R—S—S—R ′) is formed on the metal thin film. Instead of the ethanol solution, thiols may be dispersed in other alcohols. Moreover, although there is no restriction | limiting in the density | concentration of ethanol solution and immersion time, it adjusts suitably according to the density and orientation of the monomolecular film to be formed.
(4) The surface of the metal thin film on which the monomolecular film of thiols is formed in the order of ethanol and pure water is washed, and the thiols that are not bonded to the metal are washed away.
(5) If necessary, the surface of the metal thin film is dried in a nitrogen atmosphere.

  The cathode gas diffusion layer 32 constituting the cathode 24 has a cathode gas diffusion base material and a microporous layer applied to the cathode gas diffusion base material. The cathode gas diffusion base material is preferably composed of a porous body having electron conductivity, and for example, carbon paper, carbon woven fabric or nonwoven fabric can be used.

  The microporous layer applied to the cathode gas diffusion substrate is a paste-like kneaded product obtained by kneading a conductive powder and a water repellent. For example, carbon black can be used as the conductive powder. Further, as the water repellent, a fluorine resin such as tetrafluoroethylene resin can be used. It is preferable that the water repellent has a binding property. Since the water repellent has binding properties, a paste can be obtained by kneading the conductive powder and the water repellent.

  According to the fuel cell 10 according to the embodiment described above, when a hydrogen leak occurs in the membrane electrode assembly 50, the cathode catalyst is produced by the poisonous substance produced from the poisonous substance production layer 31 in the presence of hydrogen. By poisoning the metal, the output voltage of the fuel cell 10 can be lowered. Thereby, when hydrogen leak arises in the membrane electrode assembly 50, the safety of the fuel cell 10 can be improved.

  Further, according to the fuel cell 10 of the present embodiment, when hydrogen leak occurs in the membrane electrode assembly 50, the poisoning substance generation layer 31 is caused by hydrogen leak without separately installing a member such as a sensor. Since the metal catalyst is poisoned by the poisoning substance generated in this way, the safety of the fuel cell 10 can be improved with a simple configuration without increasing the size of the device configuration of the fuel cell 10.

  The present invention is not limited to the above-described embodiments, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. Embodiments to which such modifications are added Can also be included in the scope of the present invention.

  In the above embodiment, the poisoning substance generation layer 31 is formed on the entire surface between the cathode catalyst layer 30 and the cathode gas diffusion layer 32. However, the poisoning substance generation layer 31 includes the cathode catalyst layer 30 and the cathode gas. A layer structure in which the cathode catalyst layer 30 and the cathode gas diffusion layer 32 are in contact with each other may be employed in a region that is partially formed between the diffusion layer 32 and the poisoning substance generation layer 31 does not exist.

  Further, the present invention can be applied to a planar array type fuel cell in which a plurality of fuel cells 10 are arranged in a plane and the plurality of fuel cells 10 are electrically connected in series. In addition, when the fuel cell 10 is applied to a passive planar array type fuel cell that does not have an auxiliary device such as a pump, the separators may not be provided on both sides of the membrane electrode assembly 50.

DESCRIPTION OF SYMBOLS 10 Fuel cell, 22 Anode, 24 Cathode, 26 Anode catalyst layer, 28 Anode gas diffusion layer, 30 Cathode catalyst layer, 31 Toxic substance production layer, 32 Cathode gas diffusion layer, 34, 36 Separator, 50 Membrane electrode assembly

Claims (6)

An electrolyte membrane;
An anode provided on one surface of the electrolyte membrane;
A cathode provided on the other surface of the electrolyte membrane;
With
The cathode is
A cathode catalyst layer in contact with the electrolyte membrane;
A cathode gas diffusion layer;
A poisoning substance generation layer that is provided between the cathode catalyst layer and the cathode gas diffusion layer and has a compound that reacts with hydrogen to generate a poisoning substance that poisons the metal catalyst contained in the cathode catalyst layer. When,
A fuel cell comprising:   The fuel cell according to claim 1, wherein the poisoning substance is a thiol.   The fuel cell according to claim 1, wherein the poisoning substance is water-soluble. The fuel cell according to any one of claims 1 to 3, wherein the compound is represented by the following formula (1).

In formula (1), M is selected from Au, Cu, and Pt. R represents a carbon chain such as an alkyl chain. R ′ is selected from an alkyl group, an aminoalkyl group, a carboxyl group, a hydroxyl group, and a sulfo group.   The fuel cell according to claim 4, wherein the metal M in the formula (1) is fixed to the surface of the cathode gas diffusion layer.   The fuel cell according to claim 4 or 5, wherein the compound forms a monomolecular film.

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